If you would like to optimize your site performance it is key to first identify the interactions that a user could generate on it. To do so you must forget about the holistic vision of systems by the systemic vision (highly recommended to read Peter Senge’s Fifth Discipline).
The holistic vision says that in order to optimize each part of the system you need to optimize each part of the system while the systemic vision says that the important thing is to understanding and optimizing not the parts (or objects) but the interactions and not all the interactions but the one/s that are mainly constraining your website from a higher performance.
If your main website objective (every system must have a MAIN objective) is Sales Conversion, then you must find and understand what interactions that a user may generate could lead to a sale and try to optimize that interaction.
When doing that remember to focus just on the main restriction do not spend unnecessary dollars on something that will not result in higher benefits. Think about your website has a pipeline, what must flows through it is your objective (sales, registrations, etc) and nothing else than that, not pageviews, not visits, not comments…just your objective. As much of your objective flows through your structure as much it will perform.
So, go ahead, let’s fall in love with your interactions